Mechanism for transforming one form of movement into another, more particularly for use in stencil printing machines



June z, '1953 J. E. FREEBORN I 2,640,415

MEcHANIsMI-oa IRANsFoRMING oNE FORM oF MOVEMENT INIo ANOTHER. MORE PARIICULARLY FOR usE IN sIENcII. PRINTING MACHINES Filed May 29, 1951 I y WEA/Tok ./nmfs kann Henna( ATTORNEY BY LM, MQW

ATTORNE)l June 2, 1953 J. E. FREEBORN A MECHANISM FOR TRANSFORMING ONE FORM OF MOVEMENT INTO ANOTHER. MORE PARTICULARLY FOR USE IN STENCIL PRINTING MACHINES -,3 Sheets-Sheet 5 Filed May 29, 19.51

ATTORNEY Patented June 2, 1953 MECHANISM FOR. TRANSFORMING ONE FORM OF MOVEMENT IN TO ANOTHER, MORE PARTICULARLY FOR USE IN STENCIL PRINTING MACHINES James Edward Freeborn, Broxbourne,l England,

assignor to Screen Printing Machinery Limited, London, England Application May 29, 1951, Serial No. 228,832 In Great Britain May 31, 1950 13 claims.

The need sometimes arises for transforming va cyclical movement of a driving member into for such a mechanism has been encountered is a stencil printing machine of the kind having a screen frame carrier which is provided with an inking carriage, mounted for movement along the screen. The screen frame carrier is movably mounted above a printing table and is arranged to be lowered onto the table when a printing stroke is to be made, after which it is raised from the table to allow of the removal of the printed sheet and of the feeding into position on the table of a fresh sheet and is then again lowered for the next printing operation.

With one form of machine, an example of which is described in my prior application Serial No. 184,942 filed September 6, 1950, the inking carriage is arranged to make a single printing stroke along the screen frame in one direction to effect a printing operation, after which the carriage remains stationary at one end of the frame during the time that the latter is raised and lowered and a fresh sheet is fed into position. After the screen has been lowered onto this fresh sheet the inking carriage makes a return printing stroke in the opposite direction.

The raising and lowering of the screen frame 'is` preferably effected by mechanism operated from a continuously rotating shaft, such as for example by the cam mechanism described in the aforesaid application., IIt is one of theobjects lof the presentl invention to provide mechanism lwhich is adapted to be operated in synchronism` with the operation of such a shaft so as to profducethe required Aprinting stroke of the inking carriage in alternate directions, which strokes `a1je correctly synchronised with the raising and lowering of the screen frame carrier and have the required intervals or dwells between them corresponding to the Vtimes when the screen carrier is not in its printing position.

order to reduce the power required to operfate the inking carriage and to reduce the stresses f'produced in the mechanism, while at the same f time maintaining an adequate speed of operation, ,sit lispreferr ed that the operation of the' inking -`carriage should be harmonic in nature in that the Vrest to reach its maximum speed-at an intermediate point in its travel, after which it progressively decelerates until it reaches-the end of its stroke. It is one of the objects of this invention to provide mechanism for achieving this.

Although thev movement-converting vmechanism which is to be describedr is particularly applicable to the operation of the inkingcarriage in a stencil printing machine its usel is not limited to such machines. It can be applied to machines of other types-*in which a similar action is required and it is, accordingly, a more general object of the present invention to provide mechanism for'conventing a cyclical movement of any driving member, which movement may be rotary or oscillatory in character, into an intermittent oscillatory movement of a driven member Y *i According to -the y invention,` in one aspect thereof, mechanism is provided for converting a cyclical movement" of a driving member into an intermittent oscillatory movement of a driven member, comprising an actuating elementwhich isy reciprocated by the driving member and la selector member, which is operatively coupled to the driven member so as to drive the latter, wherein the selector member is provided with a pair of abutment members, eachfmovable between an operative and an inoperative' `poition, one of which members" is adapted'when-in its operative position to be engaged by the actuating element when the latter is travelling inone direction so as to operate the selector'member in that direction and the othery offwhich `relements is adapted when in its operative position to be engaged by the actuating element when the latter is travelling in the reverse-direction so as to operate the selector member in that reverse direction, and wherein means are provided operated from the driving member for moving Vthe abutment members between their operative and inoperative positions such that the selector member is operated during selected strokes only of the actuating element.

In the case of the application of the invention to astencil printing machine there is provided, according to a further aspectof this invention, a stencil printing machine comprising a frame structure carrying a printing table, a screen frame carrier movably mounted on vsaid structure for movement towards and away Vfrom the printing table, an inking carriage reciprocable along the screen frame carrier, a rotaryr driving shaft, means operated by the kdriving shaft lfor raising and lowering the screen frame carrier and mechanism operated from the shaft for reciprocating the inning carriage along the frame carrier, vvl 1eieinL the said mechanism comprises an actuating element which is reciprocated by the rotation of the driving shaft, a reciprocable selector member and means transmitting the movements of the selector member tothe inking carriage, the selector member being provided with a pair of abutment members, each movable between an operative and an inoperative position, one of which membersis adapted when in its operative position to be. engaged by the actuating element when the latter is travelling in one direction so as to operate the selector member in that direction and the other ci' which niem-V bers is adapted when in its operative position to be engaged by the actuating elemento/lien vthe latter is travelling in the reverse direction so as totoperate the selector member in that reverse Amembersbetween their operative and inoperative positions such that the selector memberis operated during selected strokes only of the actu- .atingelement, whereby the inning carriage is -causedto makesingle printing strokes in alternate directions-during the ytimes when the screen frame carrier` is in its printing position adiacent the Atable.

The movement of the selector members produced by the mechanisms referred to is reciprocatingand generally linear in character and its amount islimited by structural considerations. It `is yet-another object of this invention to provide-mechanism for converting the linear movement of the selector member into an amplified rotational movement of a rotary driven member, the extent or" which movement may amount if necessary to several complete revolutions.

In some applications of the invention this rotary movementmay be employed directly withoutffurther modification, but in the case of a stencilprintingmachine it is used to drive the 1 inningy carriage vwhichlis caused to reciprocate through-,a distance which may be substantially greatenthan the-stroke of the selector member'.

Forthebetter understanding of the invention ,the application Aof the same to the driving ofthe inning carriage of lastencil printing machine will `now/ be described. Reference will be hadto the accompanying drawings, in which:

Figure l is a general side view of a stencil printingmachine exemplifying the invention v Figure 2 is a detail view showing part of the Lmechanismfor driving the inking carriage;

Figurev 3 is a kdetail view showing parts of the mechanism of Figure 2 in the positions occupied at a laterstage'in the operation of the machine;

l'igurefln is a View similar to Figure 2 but showing a. stilllater stage in the operation.

Referring first to Figure'l, which is to some extent diagrammatic in character, the machine comprises, a frame structure l of any suitable construction which supports a printing table 2,

`agreed resistance-delivery tatie 4. The deliverytable 4 formsin effect a continuation of the surface oftheprinting table 2, as doesthe front portionand one-side of theV feed table 3. The

main part 5 ofthe feed table is, however, ar-4 rangedto be adjustable in height, part of the mechanism for raising and lowering it being indicatedat 6 in Figure l. In use a stack of sheets to be printed is placed on the part 5 of the feed table; which is progressively'raised as'printing proceeds so that the top sheet is always level with or a little above the level of the printing table.

Feed and delivery mechanism which may be of the kind described in the aforesaidy prior application is provided for drawing a sheet from the feed table 3 into the printing position on the printing table 2 and for delivering this sheet, after printing, on tothe delivery table 4.

A chain '1, which is driven through mechanism indicated diagrammatically at 8, forms part of the paper feed and delivery apparatus, which latter will not, however, be described further since it forms no'` part ofl the present invention.

Suction mechanism of the conventional type may be provided for holding the sheets down on the printing table during printing and, if desired, during the first part of the upward movement of the screen away from the table.

The stencil screen to'be used is tted in a suitable frame (not shown]I which is mountedl in a screen frame carrier indicated generally at 9. Slidably mounted on suitable rails or' guides forming part of this carrier 9 is an inkinglc'r riage I0 which is arranged tohbe Aoperat'edfby means of a pair of chains H which are provided at opposite sides of the framecarrier and'each of which is attached at .its ends to the inking carriage.

The carriage l0 is provided withV apairk of squeegees (not shown) either one ofv` whichA is arranged to be brought into engagement with the stencil screen according to the direction'of Inovement of the carriage. Automatic mechanism' of any suitable type is provided fori automatically raising one squeegee and lowering Vthe other when the carriage is at or near the limits of .its movement inopposite directions. Parts ofv this mechanism are shown at I2, I3` and I-l'but no further description of it will be given` sincey it forms no part of the present invention.

Each of ther chains H istrained about sprockets I5 and i6 mounte'dat opposite ends of'the frame carrier 9. The sprockets l5 `are idler sprockets but the two sprockets IB at'th'eV other end of the frame carrier are secured'to a shaft Il which shaft extends across the carrierl This shaft il is arranged to be driven from ashort shaft I8 by. means of a chainlS'which'S trained about sprockets mounted onV the outer" endsof these shafts. The shaft I8 itself forms a pivotal connection between the frame carrierv 9 and a bearing bracketmounted on the frame structure I of the machine at one sideof the latter', while at the other side of a machine a similar pivotal mounting for the carrier il is 'provided byneans of another shaft or pin which is similar'to the shaft :c but which forms no part ofthe-'driving mechanism.

lThe mechanism for raising .and lowering the frame carriers V9V will now" be described. This mechanism comprises a main cam shaftll ywhich is journalled in suitable bearingsprovided infthe of working of thev machine' can be adjusted as.

required;

erated as it nears the end of its travel.

.agosw :One end of the driving shaft 23 carries a sprocket 21 from which the drive is transmitted to the cam shaft 20 by means of a chain 28 which passes round a sprocket 29 mounted on the cam shaft. The sizes of the sprockets 21 and 29 are such as to provide a 3:2 speed reduction between the driving shaft 23 and the cam shaft 20.

At each of its ends the cam shaft 20 carries a cam 30, which cams engage rollers 3| which sequently as the cam shaft 20 rotates the frame carrier is raised and lowered by the action of the cams 30.

The speed with which the frame carrier 9 can be raised is limited not only by the weight and inertia of the parts concerned, but also by the fact that during the raising operation the printed sheet has to be separated with a peeling action from the underside of the screen. The lowering of the frame carrier can, however, be eected more rapidly, and the cams 30 may be appropriately shaped to give this result, while allowing the frame carrier to remain in its lower position for the period required for the printing' stroke.

Thus, to give one example, the raising of the carrier 9 may occupy 120 of the rotation of the cam shaft 20, after which the carrier is held in its raised position for a further 60 of this rotation in order to provide adequate time for the removal of the printed sheet and for the feeding of a fresh sheet on to the printing table. The next 60 of the rotation of the cam shaft effects the lowering of the carrier, after which the latter is allowed Ito remain in its lowered position for the remaining 120 of the rotation of the shaft 20, during which time the carriage lil effects a printing stroke.

It is important to note that the cam 30 should be so shaped that the raising and lowering movements of the carrier 9 are harmonic in character in that the carrier is made to accelerate progressively until it reaches its maximum speed o-f movement, after which it is progressively delrzlells greatly reduces the shocks and strains which are produced in the mechanism. The mechanism for operating the inking car riage will now be described.

This mechanism comprises a crank 40 (Figures 2 to 4) which is mounted on the driving shaft 23 of the gear box 2l on the side of the latter opposite the sprocket 21. This crank 40 -is connected at 4| to a connecting rod 42 which is provided at its other end with an actuating roller 43. With the parts in the positions shown in Figures 2 and 4 this roller 43 rests on a member 44 which is attached to a pair of parallel, substantially-horizontal selector plates 45. These plates are pivotally connected at 46 and 41 to two pivot arms 43 and 49 which are in turn pivoted at 50 and 5l to the frame of the machine. In this way the selector plates 45 are supported for limited reciprocating movement along an arcuate path between the position shown in Figures 2 and 3 and that shown in Figure 4. The amount of this movement is limited by means of adjustable stops 52 and 53 which are adapted to engage a part of the frame structure of the machine,l such as the lower edge 54 of an opening in one of the .side plates of this structure. In the construction shown the stops 52 and 53 are `constituted by screws which are mounted in a bracket 55 on the pivot arm 48 and which are provided with lock nuts 55 and 51. n

Mounted between the selector plates 45 are two abutment members 58 and 59 which are pivoted to the plates 45 at 60 and 6l respectively. The member 58 is movable between a lower inoperative position as shown in Figure 2 and anupper operative position which is shownuin kFigures 3 .and 4, while the member 59 is similarly movable roller 43 to engage the abutment member andk thereby to move the selector plates from one limit position to the other. When, however, Vone of the abutment members is in its lower position movement of the connecting rod in the direction of that member will merely cause the roller 43 to run along the upper surface of the member and the selector plates will not be operated.

The abutment members 53 and 59 are provided with spring-urged plungers 62 and 63 (Figure 2)V respectively, the ends of which plungers bear resiliently against the sides of the member 44 and are adapted when the abutment members are in their upper positions to engage in V- shaped notches 64 and 65, which notches limit the upward movement of the members 58 and 59 and tend to retain lthese members in their upper positions until they are moved from them by the mechanism now to be described.

This mechanism comprises a link 56 which is pivotally connected at its ends to upstanding stop arms 61 and 68, which latter are rigidly mounted on the abutment members 58 and 59 respectively. The length of the link 65 is such that when one abutment member is moved to its lower position, theY other abutment member is raised to its upper position, and vice versa. The positions of the stop arms B1 and 68 are such that when the roller` 43, running along the upper surface of one of the abutment members, nears the end of its stroke it engages the corresponding stop arm and rocks the latter so as to raise this abutment member while at the same time lowering `the other member (see Figure 3).

In order to ensure correct operation of the selector plates a rod 69 carrying a pair of compression springs 10 and 1l is pivotally connected at 12 to the member 44, while its lower end passes slidably through a block 13 which is pivoted at 14 to the frame I. The action of the springs 10 and 1I causes the rod 39 to urge the selector plates 45 to the right or to the left, depending on whether they are on one side or the other of their central position,

'Ihe operation ofthe above selector mechanism will be described in due course in conjunction with the remainder of the drive tothe inking me warmem@ what it wnit'his steunt is a" sbs-f r11-bralled-inbearings provided on'the'iraine of the machine'. Freely rotatable on this shaft 'Il' are an internally toothed an'ulus 'L18y and`r a planet carrier '19; Thisplanet carrier carries a number'of planet Wheelsv` 80 which lmesh with the sun- Whel 'F6V and with th annulus T8Q, l

TWO linls` arms 8l and 82 are provided, pivoted at' ISG to the selector platesli' The arm Si is connected'- at B3" to the annulus' 'itat av point above the axis' of" thev shaft Td, Whilethe' arm 82' isl connected'at M to an extension of the planet carrier '19'. As a result of this arrangement, when the selector plates ilare moved to the left thI link Sl rotates' the annulus 18" inf an anti-clockwise direction, While the link 82 rotatesY the'V planet" carrier '19""inl a' clockwise direction. These yrotations of the annulus and planetjca'rrier have'a' cumulative actionand impart to the sunwheel l'ia'fconsiderably ain'pllied rotation in a' clockwise direction;` The amount of this" rotation may amount to several rvolutions depending on the relative' sizes of the" gears involved; v

The shaft Il isconnecte'd to the shalt iS'by means .of a chain S5"Whieh'is trained about sprockets mounted'on theseshafts;` A tensioning'sprooket' may' bel'providedfor adjusting the tension 0f the chain if necessary.V l

It will be seen 'that the effect ofthe'epicyclicf mechanism just described'will be to convert the relatively short, reciprocatoiy movements o the selector plates 45 into amplifiedv movements of the''inking carriage" l@ which isther'eby caused to malte vth'e'fred' "red" printing strokesi'as will'belj '.s'c'ribedl` Iti preferredfto make tl'iesprockets carrying the chai-'nrw accessible and' readily interehan'egabl'sd-that' they can'- be chang'ed when required in order to-give a change oi ratio in the drive to thecairiage This is very advan- ,L

tageous sinceiit enables theprintiirgstr'oie to be limited' 'to the-:length: of" the particular" sh'eet loeu ing iused," WhileI infnfiiilti-co'lour printing, in which some'of the'- colours 'may be grouped'in` Vdifferent small areas'ofaflarg pr-int," the 'stroke can be limited to `cover only'tl'ie particular-"area concerned.j Theiuse 1' *the "maximum" stroke' under such-conditions wouw tewastefurmfmr' aswell as in-l the siilr 'screen material, it Would'increase thefarnount of tl'ie'preparatory Work'ne'ces'sarvingu setting up thefmachine'fand"Woultilrestrict' vthe Speeder' printingofi va smallisheet'or part off a sheet' toY that"requiredf"'for printing a 'full-sized sheet.

The operation of the screen raisingand car-,1.

riag'e` drive mechanismwill'noiv befdesciibedl lt will be assumedthalthe' partei are in the'positions shown "in" Figure 2' v'and thatf'a' printing strokel has-just been completedfso that'the frame carrier 9-is about'to befliftedby-theactionofa.

thecams' 3u. Duringftiel time 'that the cam shaftl `Eil is turning-*through 120? to" raise the frame carrier lto fthe;- start of itsdiv'ell! at thefpoint of maximum lift, the"cranl f4il'turnsthrough V180" owing to the 3:2*gearingbetvv'een' the shafts 23I4 5B untiLVas itnearsnthe engl ofits strolefit' engages 'the stop Lr'od""'$'l" and operat'esith'e-f latten lofi, a,

movementstransmmezrm themki @carriage-:f

s during the fiest lair rotation of the crank to the r'llei" 43`v11is'back" d'vv'r the left-hand abutment member untilA it drops off the end Yof the latter' on" tothe memberita, as is', insicatedin detiene-dash lines in Figure. ls. During-Y this stroke' also no movement i'sviniparted to the selector plates" and to the inkingcarriage.

vThis last 180 movement of the crankllcorresponds to'a 120i. rotation of the'camshaft 2i). During" the rst half of this rotation the frame carrier El 'is held in its -upper-'pos'iton'and .during the' second half thereof it is allowed to descend into contact with a Work sheet on the table; r'elady` for lfi'r'inting. In .its lower position theframe carriere engages fixedst'ops 8'3 mounted onthebrackets it. During the Anext half turn .of Ythe...cranlf; Mi (which correspondsto ar 120 rotation oflthe cam `shaft' 26' during which the frame .carrierviY remains'lower'ed) the tracking roller. 63 engages the end face of the abutment member '.58 (which is notv raised) and thereby` moves the selector plates 45 through one completeV stroke from right to left, thereby' bringing them'to the positionshown'in Figure 4. This movement is transmittedthrough the mechanism 'i5 to the inking carriage et which is thereby' caused to. make A a printing stroke in one direction alongV the screen. During the next half-turn of thelrcrank l2 the roller '13 runs' up'the abutment member 59,*vwithout operating the selector plates, until it engages the" stop rod 58 to reverse" the positions of the abutment members. During this time the'. cam shaft 2Q turns through the first 120 of its next complete-rotation, thus againv raising the frame drops on to the member die, afterwhich during thenext movement of the. connecting roddZ to the right the roller d3 engages the end of vthis abutment member'and moves the selector plates tothe'right. Thus in this secondV .printiifigz operation the inking" carriage it makes a printing strole in the reverse direction. v

Although" the movement-conversion or selector` mechanism of the invention,Y Which is centered about the selector plates t5, is particj'ularlvapplicable' to the driving ol'l theV inking carriage'of a screen printing. machine. and ,has been described with reference tosuch a' machine, the invention is not limited thereto.. .This mechanis'zn can be employed invv other cases in .which a similarconversion 4of oneI form of movement into another is required. It' may` be employed in conjunction with a sp'eedmultiplying mechanism', such fas is representedby the..epicyclic m''ech'sinistriV l?, or' suchmechanism may be omitted if it'is only' desired to obtain a rei, Mechanismio'r"converting a cyciicalmove- "indent 'cfa driving member into an intermittent oscillatory movement oi a driven member comprising actuating element which is reciprocated'by the driving member andra ys'elector'member which is operativelvcoupled to the driven memb'eij'so. as to 'drive thelatter, wherein the selector-membei is provided'ivith a pair of abut.. nientfmembers, eachfmovablefbetween an operative and an 'inoperativel position, onelof which members is ladapted when in its foperative f posi- :"tionto'- be'f'engaged by thev actuating element when the latter is travelling in one direction so as to operate the selector member in that direction and the other of which members is adapted when in its operative position to be engaged by the actuating element when the latter is traveiling in the reverse direction so as to operate the selector member in that reverse direction, and wherein means1 are provided operated from the driving member for moving the abutment members between theii operative and inoperative positions such that the selector member is operated during selected strokes only of the actuating element.

2. Mechanism as claimed in claim 1, wherein the abutment members are operatively coupled together such that when one member is moved to its operative position the other is moved to its inoperative position.

3. Mechanism as claimed in claim 2, wherein each abutment member is provided with a stop element which is adapted to be engaged by the actuating element and to be operated by it so as to move the said abutment member to its operative position while the actuating element is making an inoperative stroke without having i:

engaged that abutment member.

4. Mechanism as claimed in claim 1, wherein the abutment members are constituted by a pair of pivoted levers having their free ends directed towards each other in positions to be engaged by the actuating element when the appropriate lever is in its operative position.

5. Mechanism as claimed in claim l, wherein the actuating element is arranged to be reciprocated by means of a connecting rod driven from a rotating driving shaft.

6. Mechanism as claimed in claim 5, wherein the actuating element engages each of the abutment members to operate the selector member once in every three strokes of the actuating element in the appropriate direction and wherein the driving shaft is connected with a control shaft through a 3:2 speed reduction gearing such that the selector member is given a single stroke in one direction during each complete rotation of the control shaft.

7. Mechanism as claimed in claim 1, wherein the reciprocatory movements of the selector member are transmitted to a rotary driven member by means including an epicyclic gear having three elements, two of which elements are connected with the selector member so as to be turned by the latter in opposite directions such that the movements of these elements produce a cumulative movement of the third element, which latter element is connected to the driven member.

8. A stencil printing machine comprising a frame structure carrying a printing table, a screen frame carrier movably mounted on said structure for movement towards and away from the printing table, an inking carriage reciprocable along the screen frame carrier, a rotary driving shaft, means operated by the driving shaft for raising and lowering the screen frame carrier and mechanism operated from the shaft for reciprocating the inking carriage along the frame carrier, wherein the said mechanism comprises an actuating element which is reciprocated by the rotation of the driving shaft, a reciprocable selector member and means transmitting the movements of the selector member to the inking carriage, the selector member being provided with a pair of abutment members, each movable between an operative and an inoperative position, one of which members is adapted when in its operative position to be engaged by the actuating element when the latter is travelling in one direction so as to operate the selector member in that direction and the other of which members is adapted when in its operative position to be engaged by the actuating element when the latter is travelling in the reverse direction so as to operate the selector member in that reverse direction and means being provided ated from the driving shaft for moving the utment members between their operative and inoperative positions such that the selector member is operated during selected strokes only of f' the actuating element, whereby the inking carriage is caused to make single printing strokes in alternate directions during the times when the screen frame carrier in its printing position adjacent the table.

9. A stencil printing machine as claimed in claim 8, wherein the abutment members are operatively coupled together such that when one member is moved to its operative position the other is moved to its inoperative position.

1G. A stencil printing machine as claimed in claim 9, wherein each abutment member is provided with a stop element which is adapted to be engaged by the actuating element and to be operated by it so as to move the said abutment member to its operative position while the actuating element is making an inoperative stroke without having engaged that abutment member.

11. A stencil printing machine as claimed in claim 8, wherein the abutment members are constituted by a pair of pivoted levers having their free ends directed towards each other in positions to be engaged by the actuating element when the appropriate lever is in its operative position.

12. A stencil printing machine as claimed in claim 8, wherein the frame carrier is operated l from a cam shift so as to be raised and lowered once during each complete rotation thereof, wherein the actuating element engages each of the abutment members to operate the selector member once in every three strokes of the actuating element in the appropriate direction and wherein the driving shaft is connected with the cam shift through a 3:2 speed reduction gearing such that the selector member is given a single stroke in one direction during each complete rotation of the cam shaft.

13. A stencil printing machine as claimed in claim 8, wherein the means transmitting the movements of the selector member to the inking carriage include an epicyclic gear having three elements, two of which elements are connected with the selector member so as to be turned by the latter in opposite directions such that the movements of these elements produce a cumulative movement of the third element, which latter element is connected to the inking carriage.

JAMES EDWARD FREEBORN.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 659,079 Lieb Oct. 2, 1900 1,922,710 Owens Aug.. 15, 1933 2,196,678 Klopfenstein Apr. 9, 1940 2,398,379 Kenney Apr. 16, 1946 2,539,258 Lindland Jan. 23, 1951 2,574,137 Zenner Nov. 6, 1951 

